Nitroglycerin, which is a vasodilator used for more than 100 years in patients with angina, has been shown to inhibit the tendency of platelets to clump together in patients with unstable angina. We wanted to see if this is also true in patients with stable coronary artery disease. We took ten patients with coronary artery disease and during their coronary angiogram we sampled blood upstream and downstream from their coronary circulation at rest and after a two-minute episode of speeding up the heart rate to simulate exercise. We have shown in the past that this causes an increase in the tendency of the platelet to form clots. In the present study we confirmed that result and then repeated the sequence after an intravenous infusion of nitroglycerine. We found that nitroglycerin blocked partially (50%) the increase in platelet tendency to form clots in response to simulated exercise. In summary, nitroglycerine at doses that are usually taken by patients with stable coronary disease could reduce the risk of unwanted cardiovascular events like unstable angina and myocardial infarction by decreasing the tendency of the platelets to form clots.